<p>This snap tool can be used to extract one coordinate (e.g. X) from the
location of one existing entity and the other coordinate (e.g. Y) from the
location of another object. 
<br />This can for example be used to locate the center of a rectangle. 
<br />This concept is also referred to as 'combining coordinates', 'point
filtering' or 'coordinate filtering'.</p>
